Method For Protecting Cross-Ring Service in Optical Network

ABSTRACT

A method for protecting a cross-ring service in an optical network includes the steps of: determining whether a configured working path crosses different rings; and in the case that the working path crosses different rings, establishing a cross-ring protection path which bypasses an off-ring node or an on-ring node of the working path on a ring, and binding the cross-ring protection path and the working path, wherein the cross-ring protection path and the working path is bound, and thus a protection can be implemented for the cross-ring service when the off-ring node or the on-ring node fails, with a reduced occupancy of bandwidth in comparison with the conventional DNI method.

FIELD OF THE INVENTION

The present invention relates to the filed of optical communicationtechnologies, and particularly to a method for protecting a cross-ringservice in an optical network.

BACKGROUND OF THE INVENTION

The optical network topology has experienced an isolated node, a lineartopology and a ring topology. At present, many networks have beenprovided with a topology of Mesh or quasi-Mesh Network. An opticalNetwork 10 as shown in FIG. 1 includes a plurality of nodes 11interconnected by a Mesh topology. The protection switching techniquealso has developed synchronously with the evolution of networks. ITUrecommendations such as G.783, G.841, G.842 and the like provideprotection methods applicable for a Link Network and a Ring Network,such as, MSP (Multiplex. Section Protection) 1+1, MSP 1:n, UPSR(Unidirectional Path Switched Ring), BLSR (Bi-directional Line SwitchingRing), etc., which have been used wildly.

Although the Mesh Network topology has been used in an optical networksystem for some time, the protections for a transport plane mainly are alinear protection and a ring protection. The protection for a cross-ring(i.e. a protection ring) service mostly adopts a DNI (Dual-NodeInterconnection) method. However, this DNI method relatively wastesresources and also has certain demands on the network structure, thatis, a dual-node interconnection is generally required, and theconfiguration thereof is relatively complicated.

FIG. 2 shows a schematic diagram of a DNI protection with an SNCP (SubNetwork Connection Protection), wherein a ring includes nodes 21, 22, 23and a ring includes nodes 24, 25, 26 are interconnected via a pair ofnodes 23, 24 and a pair of nodes 22, 25. According to this solution,each service is adapted to an SNCP service, where a dual-transmission ofthe service must be performed on an on-ring node and two interconnectednodes of a present ring, and a selective reception of the service can beperformed on the two interconnected nodes of another ring and anoff-node of the service of another ring. Since in this solution eachcross-ring service needs the dual-transmission, a great deal ofbandwidth resources may be occupied, and the configuration process maybe very complicated. Moreover, this solution may be only applicable forthe case of the dual-node interconnection, and fail to provide aneffective protection for the case where the rings are interconnectedmerely via a single node or share no common node.

Also, a method interconnecting rings with the Multiplex Section canprovide such a protection. Generally, this method performs a servicedual-transmission on interconnected local-ring nodes, and performs aselective reception on interconnected nodes at the same side of anotherring. The configuration process for this method may be complicated whichrequires a manual configuration), and the bandwidth on a MultiplexSection ring may be occupied excessively (in particular when theinterconnected nodes are not adjacent ones on the ring). Moreover, thissolution may be only applicable for the case of a dual-nodeinterconnection, and fail to provide an effective protection for thecase where the rings are interconnected merely via a single node orshare no common node.

SUMMARY OF THE INVENTION

The present invention provides a method for effectively protecting across-ring service in an optical network to overcome disadvantages of alow bandwidth utilization ratio and a strict requirement on the networktopology in connection with the Dual-Node Interconnection method in theprior art used for the cross-ring service.

An embodiment of the present invention provides a method for protectinga cross-ring service in an optical network, wherein the method mayinclude the steps of:

determining whether a configured working path crosses different rings;and

in the case that the working path crosses different rings, establishinga cross-ring protection path which bypasses an off-ring node or anon-ring node of the working path on a ring, and binding the cross-ringprotection path and the working path.

Preferably, the method may further include the steps of:

selecting a first node, other than the off-ring node, on a first ringincluding a service transmitting node, and selecting a second node,other than the on-ring node, on a second ring including a servicereceiving node, wherein the first node and the second node are locatedon the working path;

establishing the cross-ring protection path with the first node being asan origination node and the second node being as a termination node; and

binding the cross-ring protection path and a corresponding protectedsection of the working path, wherein the origination node and thetermination node of the protected section are respectively the firstnode and the second node, and the protected section includes theoff-ring node or the on-ring node.

Preferably, the cross-ring protection path may be established throughResource Reservation Protocol-Traffic Engineering Protocol, OpenShortest Path First-Traffic Engineering Protocol or IntermediateSystem-Intermediate System-Traffic Engineering Protocol.

Preferably, the method may further include the step of:

a node for selectively receiving a service on the working path and thecross-ring protection path performing a transfer for a point ofselectively receiving a service according to a ring switching status.

Preferably, in the case that the ring in which the node for a selectivereception is located operates normally, the node for a selectivereception may selectively receive a service on the working path and thecross-ring protection path.

Preferably, in the case that a section protection switching occurs tothe ring in which the node for a selective reception is located, thenode for a selective reception may selectively receive a service on anon-ring identical-direction protection path in the and the cross-ringprotection path.

Preferably, in the case that a ring protection switching occurs to thering in which the node for a selective reception is located, the nodefor a selective reception may selectively receive a service on anon-ring opposite-direction protection path in the and the cross-ringprotection path.

Preferably, a 1+1 or 1:1 protection may be adopted for the working pathand the cross-ring protection path.

Preferably, the working path may cross rings interconnected via a singlenode or dual nodes or without a common node.

According to the method for protecting a cross-ring service in anoptical network in the embodiments of the present invention, with anestablishment of a cross-ring protection path and a binding between thecross-ring protection path and a working path, a protection can beimplemented for a service crossing rings interconnected via a singlenode. Moreover in comparison with the conventional Dual-NodeInterconnection, the embodiments of the present invention can reduce theoccupancy of bandwidth resource on the Multiplex Section and improve thebandwidth utilization ratio. In addition, the embodiments of the presentinvention can provide a protection for a service crossing ringsinterconnected via dual nodes or without an interconnecting node, thusenabling an effective protection for a cross-ring service in an opticalnetwork.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a schematic diagram of a Mesh Network topology in the priorart;

FIG. 2 is a schematic diagram of a Dual-Node Interconnection of a SubNetwork Connection Protection ring according to the prior art;

FIG. 3 is a schematic diagram of a layered architecture of an opticalnetwork;

FIG. 4 is a schematic diagram of a service path according to anembodiment of the present invention;

FIG. 5 is a structural schematic diagram of node G shown in FIG. 4;

FIG. 6 is a flow chart of a method for protecting a cross-ring servicein an optical network according to an embodiment of the presentinvention; and

FIG. 7 is a detailed flow chart of the step of planning a cross-ringprotection path shown in FIG. 6.

DETAILED DESCRIPTIONS OF THE EMBODIMENTS

The present invention will be further described hereinafter withreference to the drawings and the embodiments so as to make theprinciple, characteristics and advantages thereof more apparent.

As shown in FIG. 3, an optical network generally includes three logicalplanes, i.e. Transport Plane 33, Control Plane 32 and Management Plane31. Control Plane 32 and Transport Plane 33 are connected respectivelywith Management Plane 31, and are connected with each other viaConnection Control Interface 34.

Transport Plane 33 includes transport network nodes 331 which areswitching entities and interconnected through Sub Network Connection332. Transport Plane 33 generally performs the functions ofconnecting/disconnecting, switching (routing), transporting and the likeso as to provide a unidirectional or bi-directional informationtransport from one end point to another as well as a transport of somecontrol information and network management information.

Control Plane 32 performs the functions of call control, connectioncontrol and the like within an intelligent optical network. ControlPlane 32 is supported by a signaling network and includes a plurality offunctional components, such as a group of communication entities,Control Unit 322 (e.g. an optical connection controller) and acorresponding internal network node interface 324. The communicationentities and Control Unit 322 respectively compose a plurality ofManagement Domains 321 interconnected via an external network nodeinterface 323. The communication entities and Control Units 322 areprimarily used for transferring a transport network resource and providethe functions related to establishing, maintaining and disconnecting(releasing the network resource) a connection. Among these functions,the functions of signaling and routing are the most important. Inaddition, Control Plane 32 is also connected to Request Proxy 36 via UNI(User Network Interface). A method for protecting a cross-ring serviceaccording to an embodiment of the present invention is implemented byControl Plane 32.

Management Plane 31 manages Control Plane 32 and Transport Plane 33.While managing an optical transport network and the nodes 331,Management Plane 31 provides an efficient communication function betweena network operation system and the nodes 331.

FIG. 4 is a schematic diagram of a service path according to anembodiment of the present invention. A solid line in the figureindicates a path with a ring protection, and a dashed line indicates apath without a ring protection. As shown, nodes A, B and E form a firstring, nodes E, F, H, I, J and G form a second ring, and the first ringand the second ring are interconnected via single node E.

It can be assumed that a service goes via four nodes A, E, G and J. Theservice can obtain a good protection respectively in the first ring andthe second ring. For example, when fiber section AE in the first ringbreaks, a service protection can be implemented via ABE, or when node Gin the second ring fails, a service protection can be implemented viaEFHIJ. However, if interconnecting node E fails, the service can notobtain a good protection. The service cannot be protected even with aDual-Node Interconnection (DNI) method, because there is one common nodeE between the two rings.

Referring to FIG. 6, it is a flow chart of a method for protecting across-ring service in an optical network according to an embodiment ofthe present invention. When configuring a cross-ring protection path,Control Plane 32 firstly configures a working path, i.e. path AEGJ inFIG. 4 (step S61). The configuration for the working path can beperformed though Resource Reservation Protocol-Traffic Engineering(RSVP-TE) Protocol, Open Shortest Path First-Traffic Engineering(OSPF-TE) Protocol, Intermediate System-Intermediate System-TrafficEngineering (ISIS-TE) Protocol and the like of GeneralizedMulti-Protocol Label Switching (GMPLS). Upon completion of the workingpath configuration, Control Plane 32 determines whether the working pathcrosses different rings, i.e., whether a service transmitting node and aservice receiving node are located in the same ring (step S62).

If the service transmitting node and the service receiving node arelocated in the same ring, it goes to step S65 of planning a MultiplexSection protection respectively within the two rings, otherwise ControlPlane 32 plans a cross-ring protection route at two adjacent nodes onthe working path on both sides of node E that interconnects the tworings (through RSVP-TE, OSPF-TE or ISIS-TE Protocol), establishes across-ring protection path bypassing node E based upon a practical usestatus of bandwidth, and binds the cross-ring protection path and acorresponding section of the working path, wherein the correspondingsection of the working path and the cross-ring protection path have thesame origination node and include node E (step S63), as will bedescribed in detail with reference to FIG. 7. When the common node ofthe two rings (node E in FIG. 4) fails, a cross-ring service 1+1protection can be implemented through the cross-ring protection path(e.g. path AFG), wherein the service is transported simultaneously ontwo channels/links which do not intersect (the working channel/link andthe protection channel/link), and thus those high-quality signals can beselected at the receiving end. 1:1 protection can also be implemented,wherein the service is only transported on the working channel/link, andthe protection channel/link does not transport a service or transports aservice with a low priority; and when the working channel/link fails,the service can be switched from the working channel/link to theprotection channel/link, and the low-priority service on the protectionchannel/link may be dropped. When a fiber breaks somewhere in the ring,a service protection (Multiplex Section protection) can be performedwithin the ring. Practically, the order of planning a Multiplex Sectionprotection within a ring and planning a cross-ring protection path canbe contrary to that as shown in FIG. 6.

Referring to FIG. 7, it is a detailed flow chart of step of planning across-ring protection path shown in FIG. 6. Firstly, a first node, otherthan an off-ring node (node E in this embodiment), is selected in thefirst ring, and a second node, other than an on-ring node (also node Ein this embodiment), is selected in the second ring. Referring to FIG.4, it can be assumed that AF and FG have available bandwidth resources,and the first node can be node A and the second node can be node G,wherein the first node and the second node are located on the workingpath, i.e., path AEGJ (step S71). Control Plan 32 can establish across-ring protection path from the first node (node A) to the secondnode (node G) (step S72), and bind the cross-ring protection path AFGand the section AEG of the working path, and thus the 1+1 protection canbe implemented for the path between AFG and AEG (step S73).

Practically, if AB and BG have available bandwidth resources, then thefirst node may be node A, the second node may be node G, and thecross-ring protection path may be path ABG. In addition to the firstnode and the second node, the cross-ring protection path can include aplurality of intermediate nodes. The configuration for the protectionpath can be achieved through such techniques as OSPF-TE (Open ShortestPath First-Traffic Engineering) or the like based upon constraintinformation of each link, the use status of bandwidth and the like

In addition, when the service is transported through rings which areadjacent indirectly, the service protection can also be achieved throughthe above method. The difference is that the off-ring node and theon-ring node are not coincident.

It can be assumed that the cross-ring protection path is path AFG, and adual-transmission of the service can be performed at node A, and aselective reception of the service can be performed at node G. When thecommon node E of the first ring and the second ring fails, path AFG maytake the place of path AEG for a service path switching.

When a section switching or ring switching occurs due to a failure ofsection EG for the second multiplex ring EFHIJG, a transfer for a pointselectively receiving the service may be required, that is, node G isrequired to select a high-quality service for a selective reception fromthe service on protection channel E-F-H-I-J-G corresponding to workingpath EG after the switching and the service on path AFG, as detailedprocess in FIG. 5.

In FIG. 5, node G includes Service Transceiver Module 41, and isconnected with a westward working channel 42, a westward protectionchannel 43 (a protection channel within the ring, which has an identicaldirection), an eastward working channel 45 and an eastward protectionchannel 46 (a protection channel within the ring, which has an oppositedirection). Here, when working channel AEGJ is in a normal status, theservice is transported in the westward working channel 42; when thesection switching occurs on section EG for the second ring EFHIJG, theservice on working path AEGH may be switched to the westward protectionchannel 43, and all the services from G to J on the second ring EFHIJGmay be transported on the eastward working channel 45; and when the ringswitching occurs on section EG for the second ring EFHIJG, the servicefrom E to G may be received on the eastward protection channel 46. Inaddition, node G is connected with the cross-ring protection channel 44so as to achieve a protection for a cross-ring service when node E forinterconnecting rings fails.

Therefore, node G receives selectively the services in FIG. 4 the way asfollowing: when no protection switching occurs on section EG of thesecond ring EFHIJG, Service Transceiver Module 41 selects and receives aservice from the westward working channel 42 and the westward protectionchannel 43, and transfers the service to the eastward working channel45; when the section protection switching occurs on section EG of thesecond ring EFHIJG, Service Transceiver Module 41 selects and receives aservice from the westward protection channel 43 and the cross-ringprotection channel 44, and transfers the service to the eastward workingchannel 45; and when the ring protection switching occurs on section EGof the second ring EFHIJG, Service Transceiver Module 41 selects andreceives a service from the cross-ring protection channel 44 and theeastward protection channel 46, and transfers the service to theeastward working channel 45.

As shown in FIG. 4, in the case of using the conventional Dual-NodeInterconnection, the resource on path ABEFHIJ has to be occupied inorder to achieve a protection for the service on cross-ring path AEGJ.Moreover, the Multiplexing Section protection (protection for path ABEand protection for path EFHIJ, respectively) is also provided in each ofthe two rings (ring ABE and ring EGJIHF). Thus, in order to achieve theprotection for the service on cross-ring path AEGJ, the bandwidth onpath ABEFHIJ has to be occupied twice that for the service. However, themethod according to the embodiment of the present invention only adoptsone service channel and one protection channel as described above, andtherefore when working path AEGJ is in a normal status, the service istransferred in a working path and when the ring fails, a correspondingsection switching is performed so as to switch the service on the failedworking path to a corresponding protection path. Therefore, it is merelyto occupy a service-corresponding bandwidth on working path AEGJ (or acorresponding protection path in the ring) or path AFG.

The present invention has been described and illustrated by way of theembodiments of the present invention with reference to the drawings, itshall be recognized by those skilled in the art that those embodimentsand drawings are merely illustrative and not restrictive, that thepresent invention shall be not limited thereto, and that variousmodifications and variations can be made thereto in light of thedescriptions and the drawings without departing from the sprit and scopeof the present invention as defined by the accompanying claims.

1. A method for protecting a cross-ring service in an optical network,wherein comprising the steps of: determining whether a configuredworking path crosses different rings; and in the case that the workingpath crosses different rings, establishing a cross-ring protection pathwhich bypasses an off-ring node or an on-ring node of the working pathon a ring, and binding the cross-ring protection path and the workingpath.
 2. A method for protecting a cross-ring service in an opticalnetwork according to claim 1, wherein further comprising the steps of:selecting a first node, other than the off-ring node, on a first ringcomprising a service transmitting node, and selecting a second node,other than the on-ring node, on a second ring comprising a servicereceiving node, the first node and the second node being located on theworking path; establishing the cross-ring protection path with the firstnode being as an origination node and the second node being as atermination node; and binding the cross-ring protection path and acorresponding protected section of the working path, wherein theorigination node and the termination node of the protected section arerespectively the first node and the second node, and the protectedsection comprises the off-ring node or the on-ring node.
 3. A method forprotecting a cross-ring service in an optical network according to claim1, wherein the cross-ring protection path is established throughResource Reservation Protocol-Traffic Engineering Protocol, OpenShortest Path First-Traffic Engineering Protocol or IntermediateSystem-Intermediate System-Traffic Engineering Protocol.
 4. A method forprotecting a cross-ring service in an optical network according to claim1, further comprising the step of: a node for selectively receiving aservice on the working path and the cross-ring protection pathperforming a transfer for a point of selectively receiving a serviceaccording to a ring switching status.
 5. A method for protecting across-ring service in an optical network according to claim 4, furthercomprising the step of: in the case that the ring in which the node fora selective reception is located operates normally, the node for aselective reception selectively receiving a service on the working pathand the cross-ring protection path.
 6. A method for protecting across-ring service in an optical network according to claim 4, whereinin the case that a section protection switching occurs to the ring inwhich the node for a selective reception is located, the node for aselective reception selectively receives a service on an on-ringidentical-direction protection path and the cross-ring protection path.7. A method for protecting a cross-ring service in an optical networkaccording to claim 4, wherein in the case that a ring protectionswitching occurs to the ring in which the node for a selective receptionis located, the node for a selective reception selectively receives aservice on an on-ring opposite-direction protection path and thecross-ring protection path.
 8. A method for protecting a cross-ringservice in an optical network according to claim 1, wherein a 1+1 or 1:1protection is adopted for the working path and the cross-ring protectionpath.
 9. A method for protecting a cross-ring service in an opticalnetwork according to claim 1, wherein the working path crosses ringsinterconnected via a single node or dual nodes or without a common node.